The production of isolated photons in PbPb and pp collisions at √s_NN = 5.02 TeV


The transverse energy ( ({E}{T}^{\gamma }) ) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at (\sqrt{{s}{\mathrm{NN}}}) = 5.02 TeV with integrated luminosities of 27.4 pb(^{−1}) and 404 μb(^{−1}) for pp and PbPb data, respectively. The results are presented for photons with 25 < ({E}_{T}^{\gamma }) < 200 GeV in the pseudorapidity range |η| < 1.44, and for different centrality intervals for PbPb collisions. Photon production in PbPb collisions is consistent with that in pp collisions scaled by the number of binary nucleon-nucleon collisions, demonstrating that photons do not interact with the quark-gluon plasma. Therefore, isolated photons can provide information about the initial energy of the associated parton in photon+jet measurements. The results are compared with predictions from the next-to-leading-order jetphox generator for different parton distribution functions (PDFs) and nuclear PDFs (nPDFs). The comparisons can help to constrain the nPDFs global fits.

High Energy Physics - Experiment, Nuclear Experiment, Hadron-Hadron scattering (experiments), Heavy-ion collision, Photon production
Sirunyan, A. M., Tumasyan, A., Adam, W., Ambrogi, F., Bergauer, T., Dragicevic, M., Erö, J., Escalante Del Valle, A., Flechl, M., Frühwirth, R., Jeitler, M., Krammer, N., Krätschmer, I., Liko, D., Madlener, T., Mikulec, I., Rad, N., Schieck, J., … Trembath-reichert, S. (2020). The production of isolated photons in PbPb and pp collisions at $ \sqrt{s_{\mathrm{NN}}} $ = 5.02 TeV. In Journal of High Energy Physics (Vol. 2020, Issue 7). Springer Science and Business Media LLC.